Many orthopaedic procedures involve the implantation of prosthetic devices to replace badly damaged or diseased bone tissue. Common orthopaedic procedures that involve prosthetic devices include total or partial hip, knee and shoulder replacement. For example, a hip replacement often involves a prosthetic femoral implant. The femoral implant usually includes a rigid stem that is secured within the natural femur bone tissue. The femoral implant further includes a rounded head that is received by, and may pivot within, a natural or artificial hip socket. Shoulder replacement is somewhat similar, and typically includes a humeral implant that includes a rigid stem and a rounded head. The rigid stem is secured within the natural humerus bone tissue and the rounded head is pivotally received by a shoulder socket.
Increasingly, prosthetic devices are provided as subcomponents that are assembled during surgery. In particular, the different anatomies of different patients require that prosthetic devices such as femoral and humeral implants be available in different sizes and configurations. By way of simplified example, a humeral implant may be available in as many as six or more humeral head diameters. Stems may similarly vary in size and/or in shape. Because the appropriate overall configuration of the implant can typically only be determined during the surgical procedure, it is advantageous that many configurations and sizes of implants be at the disposal of the surgeon. Instead of providing a separate implant for each possible combination of features, implants are provided as modular kits of subcomponents that allow the surgeon to mix and match different subcomponents to achieve the most advantageous combination for the patient. Thus, the surgeon can pick from several sizes or configurations of each component and combine the components to form an implant having an optimal combination of features.
One example of a modular implant is the femoral implant 10 shown in FIG. 1. The femoral implant 10 includes a femoral head 12 that may be assembled onto a femoral stem 14. The femoral stem 14 is configured to be implanted in the intramedullary tissue of a natural femoral bone, while the femoral head 12 is configured to be received into an acetabular cup implanted into the acetabulum. The femoral stem 14 includes a tapered plug 16 that is designed to be received by a tapered receptacle 18 in the femoral head 12. It can be appreciated that the surgeon may secure alternative femoral head designs on the same femoral stem 14, thus providing the surgeon with a broad array of femoral head size options.
Once the components are selected, such as the femoral head 12 and the femoral stem 14 of FIG. 1, then the components are assembled either externally or in vivo. A popular method of securing implant components together involves the use of a Morse taper. The components of FIG. 1 by way of example include a Morse taper arrangement. In particular, a Morse taper is a feature in which a tapered male component, e.g. the tapered plug 16, is received into a tapered female component, e.g. the receptacle 18. The taper angle of the plug 16 is preferably, but need not be, slightly less than the taper angle of the receptacle 18. In use, the plug 16 advances into the receptacle 18 until it begins to engage the receptacle 18. The further into the receptacle the plug 16 is forced, the more tightly it engages.
The force applied to secure the plug 16 within the receptacle 18 is proportional to the retention force of the plug 16 within the receptacle 18. Thus, if a sufficient amount of force is applied, then the femoral head 12 will be securely fastened on the femoral stem 14. Other prosthetic devices employ Morse tapers for substantially the same reasons.
To apply sufficient force to lock the Morse taper arrangement, it is known to impact the femoral head 12 such that the impact force directs the femoral head 12 toward the femoral stem 14. The impact force drives the plug 16 into the receptacle 18 and forms the Morse taper lock. A hammer or mallet is typically struck directly on the head 12, or through an impacting plate, tool or mechanism.
Previously, the surgeon (or other person) would impact a prosthetic implant several times without knowing if the necessary force had been applied to lock the Morse taper sufficiently. Often, in order to be sure that the Morse taper had locked, the surgeon or assistant would use excessive force. The use of excessive force is undesirable because of the potential for damage to the bone tissue or the implant device.
Although some surgeons have developed a feel or instinct as to the amount of force that is needed to form a Morse taper lock when dealing with replacement components made from more traditional materials such a cobalt chrome, there is a relatively recent movement toward the use of ceramic replacement components. While providing many benefits over replacement components made from, for example, cobalt chrome, the ceramic components are generally more brittle. Accordingly, even surgeons adept at forming Morse taper locks using materials such as cobalt chrome may use excessive force when attempting to form a Morse taper lock with a ceramic replacement part.
Thus, there is a need for assisting surgical personnel in ensuring that sufficient force has been applied to a Morse taper to lock the Morse taper while avoiding excessive force. Such need is widespread as Morse tapers have commonly been used for connection of many types of implant devices. Moreover, there is a need for assisting surgical personnel in determining whether sufficient force has been applied to a Morse taper to lock the Morse taper when the replacement components are made from different materials. There is further a need for ensuring that sufficient force has been applied to a Morse taper to lock the Morse taper for replacement components of different sizes.